Toner and developer for developing electrostatic image and image forming method

ABSTRACT

A toner for developing an electrostatic image is disclosed. The toner contains an amount of not less than 0.1% by weight of an element selected from elements of the Groups of 1B, 2B, 4B, 5B, 6B, 7B, 8, 3A and 4A of the fourth and fifth periodic of the long periodic table of the elements, and the isolation ratio of the element is not more than 10% by number.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a continuation of U.S. patent application Ser. No.09/505,459, filed Feb. 11, 2000 now abandoned, the entire contents ofwhich are incorporated herein by reference.

FIELD OF THE INVENTION

The invention relates to a toner for developing an electrostatic image,a developer comprising the toner and an image forming method using thedeveloper.

BACKGROUND OF THE INVENTION

Generally, in an electrophotographic method utilized for image formationby a copying machine, a static charge is uniformly formed on the surfaceof a photoreceptor having a photoreceptive layer composed of aphotoconductive material. Then a electrostatic image corresponding tothe image to be formed is made on the surface of the photoreceptor byimagewise exposing to light. The electrostatic image is developed by adeveloper to form a toner image. The toner image is transferred to arecording medium such as paper and fixed.

Many characteristics are required to the developer to be used for theelectrophotographic method. For example, a coloring ability, suitableelectrostatic, thermal, mechanical and chemical properties, a suitablefluidity, an anti-blocking property and a powder property relating tothe particle size distribution are required to the toner in thedeveloper. The toner is comprised of a binder resin and a complex fineparticle which is composed of a colorant and various materials forsatisfying such the requirements.

When the image forming operation are repeatedly performed using such thedeveloper, it is often observed that a charge providing member such as acarrier and a blade for forming a thin layer of developer wascontaminated by a part of the materials constituting the toner, with theresult that the static property of the toner is changed and a badinfluence is occurred on the image quality. However, the materialcontaminating the charge providing member is various since the toner isconstituted with various kinds of material. Accordingly, any simplerelation cannot be found between the amount of the contaminatingmaterial and the variation of the charging property. As a result ofthat, effective countermeasure cannot be taken in the present condition.

SUMMARY OF THE INVENTION

The first object of the invention is to provide a toner for developingelectrostatic image by which the change in the charging property causedby contamination of the charge providing member is inhibited when theimage formation is continued for a long period of time, and stableimages are formed for many times of image formation.

The second object of the invention is to provide a developer fordeveloping electrostatic image by which the change in the chargingproperty caused by contamination of the charge providing member isinhibited when the image formation is continued for a long period oftime, and stable images are formed for many times of image formation.

The third object of the invention is to provide an image forming methodfor developing electrostatic image by which the change in the chargingproperty caused by contamination of the charge providing member isinhibited when the image formation is continued for a long period oftime, and stable images are formed for many times of image formation.

The toner for developing an electrostatic image of the inventioncontains an amount of not less than 0.1% by weight of an elementselected from the elements of the Groups of 1B, 2B, 4B, 5B, 6B, 7B, 8,3A and 4A of the fourth and fifth periodic of the long periodic table ofthe elements, and the isolation ratio of the element is not more than10% by number.

In the toner for developing electrostatic image of the invention, theisolation ratio of the element is preferably not more than 5% by number,more preferably not more than 2.5% by number.

When the developer is a single-component developer, the developercontains the above-mentioned toner for developing electrostatic image.

When the developer is a two-component developer, the developer containsthe above-mentioned toner for developing electrostatic image and acarrier.

The image forming methods comprises the steps of forming anelectrostatic image on the surface of a photoreceptor, developing theelectrostatic image by a developer to form a toner image, transferringthe developed toner image to a recording medium and fixing the tonerimage transferred on the recording medium, in which the above-mentioneddeveloper for developing electrostatic image is used.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 is a scheme of a developing section for non-contacting developingmethod.

DETAILED DESCRIPTION OF THE INVENTION

Toner for Developing Electrostatic Image

The toner for developing electrostatic image of the invention basicallycomprises a colored particle containing a binder resin, a colorant andan elements selected from those of Groups 1B, 2B, 4B, 5B, 6B, 7B, 8, 3Aand 4A of the fourth and fifth periodic of the long periodic table ofthe elements in an amount of not less than 0.1% by weight.

Concrete examples of preferable such the element, hereinafter referredto the specified element, are copper, chromium, iron, zinc andmolybdenum. Although the function of the specified element has not beenconfirmed, a large triboelectricity generating ability is given to thetoner by the existence of a small amount of the element in the isolatedstate since the element has a strong triboelectricity giving abilitycaused by the atomic structure of the element itself. It is presumed,therefore, that the specified element in the isolated state stronglycontributes to the stability of the electricity ability of the developerfor a long period of time.

The specified element can be contained in the toner, for example, in aform of pigment, charge controlling agent or metal oxide, although maybe contained in a form of elemental metal. Concretely, the specifiedelement can be contained by adding into a component of toner, forexample, a pigment such as copper phthalocyanine pigment, a magneticpowder such as magnetite and ferrite, and a charge controlling agentsuch as an chromium azo complex, a chromium salicylic acid complex, azinc salicylic acid complex, a zinc salicylic acid complex and amolybdenum quaternary ammonium complex.

The content of the specified element in the toner can be measured by anordinary element analyzing method, preferably by a fluorescent X-rayanalyzing method. In concrete, the element in the toner is qualitativelyanalyzed by using fluorescent X-ray and a quantitative curve is drawn atthe same time. The content of the specified element in the toner can bedefined by the quantitative analysis of the specified element accordingto the quantitative curve.

In the toner for developing electrostatic image according to theinvention, the isolation ratio of the specified element is not more than10%, preferably not more than 5%, more preferably not more than 2.5%, bynumber.

When such the condition is satisfied, the amount of the materialcontaining the specified element transferred to the charge providingmember is inhibited. As a result, the variation of the charging propertyof the toner is inhibited and many images can be stably formed even whenthe image formation is continuously repeated for a long period.

When the isolation ratio of the specified element exceeds 10% by number,various problems are raised since the variation in the electricity ofthe toner is become relatively large when the image formation using suchthe toner is repeated for a long period of time.

The lower limit of the isolation ratio of the specified element is 0.1%by number. When the ratio is less than 0.1% by number, the electricityof the toner is lowered since the electricity giving ability of thespecified element is become insufficient.

The “isolation ratio” of the specified element is a ratio (% by number)of the number of the particles containing the specified element otherthan the colored particle, for example, particles of the magneticsubstance and the charge controlling agent, to the whole number ofparticles of the toner.

The isolation ratio of the specified element can be measured by thefollowing procedure.

The toner is sampled on a filter using a low volume sampler. The sampledtoner is rapidly sucked by an aspirator to separate to individual theparticle. The particles are introduced into He microwave plasma to besubjected to an emission spectrographic analysis. In the emissionspectrographic analysis, plural spectroscopes are used so that carbonand the specified element contained in an amount not less than 0.1% byweight can be detected by fluorescent X-ray analysis. Then the resultsof the spectrographic analysis are checked so as to classify theparticles to synchronous light emission particles and non-synchronouslight emission particles. When a particle emits light, the particle is asynchronous light emission particle if both of light caused by carbonatom and that caused by the specified element are observed at the sametime, and the particle is a the non-synchronous light emission particleif both of light caused by carbon atom and that caused by the specifiedelement are not observed at the same time.

The number of the particle containing the specified element whichsynchronously emits light caused by the specified element with lightcaused by carbon atom, hereinafter referred to as synchronous lightemission particle, and the number of the particle containing thespecified element which emits light caused by the specified elementwithout synchronous light emission caused by carbon atom, herein afterreferred to as non-synchronous light emission particle, are counted. Theratio of the number of non-synchronous light emission particle to thesum of the number of the synchronous and non-synchronous light emissionparticle is defined as the isolation ratio of the specified element inpercent by number.

In the above procedure, Particle Analyzer PT-1000, manufactured byYokogawa Denki Co., Ltd., can be used for fluorescent analyzing theparticles constituting the toner.

The toner for developing electrostatic image according to the inventionmay be one prepared by melting and kneading the binder resin, colorantand an internal additive to be added by necessity and crushing andclassifying the kneaded product, hereinafter referred to Toner A, or oneprepared by a polymerization method, hereinafter referred to Toner B.

Toner A

A binder resin to prepare the Toner A, such as a styrene resin, an acrylresin, a styrene/acryl resin and a polyester resin, is usable for thebinder resin of the toner of the invention.

A colorant to prepare the Toner A, such as carbon black, a magneticmaterial, a dye and a pigment, is usable for the colorant of the toner.

Examples of the carbon black usable as the colorant include channelblack, furnace black, acetylene black, thermal black and lump black.

Examples of the magnetic substance include a ferromagnetic metal such asiron, nickel and cobalt, an alloy containing such the metal, a compoundof a ferromagnetic metal such as ferrite and magnetite, a ferromagneticalloy by a heat treatment even though containing no ferromagnetic metalsuch as a kind of alloy called Heuslar alloy such asmanganese-copper-aluminum and manganese-copper-tin, and chromiumdioxide.

As the dye, for example, C.I. Solvent Red series of 1, 49, 52, 58, 63,111, and 122, C.I. Solvent Yellow series of 19, 44, 77, 79, 81, 82, 93,98, 103, 104, 112 and 162, and C.I. Solvent Blue series of 25, 36, 60,70, 93 and 95, are usable. A mixture of them may also be used.

Examples of the pigment include C.I. Pigment Red series of 5, 48:1,53:1, 57:1, 122, 139, 144, 149, 166, 177, 178 and 222, C.I. PigmentOrange series of 31 and 43, C.I. Pigment Yellow series of 14, 17, 93, 94and 138, C.I. Pigment Green 7, C.I. Pigment Blue series of 15:3 and 60.These pigments may be used singly or in combination.

Number average of primary particle diameter of the colorant, which mayvary depending on the species, is preferably about 10 to 200 nm.

The amount of the colorant is not particularly specified as far as it issufficient to form images, and 1 to 10 weight percent in, the Toner A ispreferable.

Examples of internal additive to be added in the toner include areleasing agent, a charge controlling agent, etc.

Practical examples of the releasing agent include polyolefin compoundssuch as low molecular weight polypropylene having number averagemolecular weight of 1,500 to 9,000, low molecular weight polyethylene,ethylene-propylene copolymer, microcrystaline wax, Carnauba wax, Sazolewax, paraffin wax, amide wax etc.

Practical examples of the charge controlling agent include a negativecharge controlling agent an azo metal complex such as azo chromiumcomplex, a salicylic chromium complex, a salicylic zinc complex and acalixarene compound, a positive charge controlling agent such as aNigrosine dye and a quaternary ammonium salt, etc.

In Toner A, the isolation ratio of the specified element can becontrolled by changing conditions of the crushing or the classification.The isolation of the specified element can be inhibited when thecrushing is performed under a mild condition so as to inhibit crushingat the interface between the substance containing the specified elementand the resin. Particularly, a mechanical crushing method is preferablesince crushing at die interface is difficultly occurred and theformation of the isolated matter can be inhibited by such the methodcompared with an air-current crushing method. Examples of the mechanicalcrushing apparatus include TURBOMILL, manufactured by Turbo Kogyo Co.,Ltd., and CRYPTRON manufactured by Kawasaki Juko Co., Ltd. In theclassifying process, a suitable isolation ratio can be obtained byrepeating the classification while feedbacking the result of monitoringon the final isolation ratio.

Toner B Various methods for polymerization method to prepare the Toner Bcan be employed. The preferable example is emulsion polymerization,particularly the method of the following (1) and (2).

(1) The toner of the present invention is prepared by employing thefollowing method. Polymer particles containing a colorant are preparedby emulsion polymerization in aqueous dispersion containing the colorantand additives added if necessary. Coagulated polymer particles areformed by adding a coagulant in an amount of more than the criticalcoagulation concentration and organic solvents which are infinitelysoluble into the obtained dispersion so that the polymer particles areassociated. The resultant is heated at least to the glass transitiontemperature of the polymer.

(2) The toner of the present invention is prepared employing thefollowing method. Polymer particles are prepared by emulsionpolymerization in aqueous dispersion containing additives added ifnecessary. Coagulated polymer particles are formed by adding a coagulantin an amount of more than the critical coagulation concentration andorganic solvents which are infinitely soluble into the obtaineddispersion and colorant so that the polymer particles are associated.The resultant is heated at least to the glass transition temperature ofthe polymer.

The method (1) is preferred to (2).

Employed polymerizable monomers to constitute a resin include styrenesor styrene derivatives such as styrene, o-methylstyrene,m-methylstyrene, p-methylstyrene, α-methylstyrene, p-chlorostyrene,3,4-dichlorostyrene, p-phenylstyrene, p-ethylstyrene,2,4-dimethylstyrene, p-tert-butylstyrene, p-n-hexylstyrene,p-n-octylstyrene, p-n-nonylstyrene, p-n-decylstyrene,p-n-dodecylstyrene; methacrylic acid ester derivatives such as methylmethacrylate, ethyl methacrylate, n-butyl methacrylate, isopropylmethacrylate, isobutyl methacrylate, t-butyl methacrylate, n-octylmethacrylate, 2-ethylhexyl methacrylate, stearyl methacrylate, laurylmethacrylate, phenyl methacrylate, diethylaminoethyl methacrylate,dimethylaminoethyl methacrylate, and the like; acrylic acid esterderivatives such as methyl acrylate, ethyl acrylate, isopropyl acrylate,n-butyl acrylate, t-butyl acrylate, isobutyl acrylate, n-octyl acrylate,2-ethylhexyl acrylate, stearyl acrylate, lauryl acrylate, phenylacrylate, and the like; olefins such as ethylene, propylene,isobutylene, and the like; halogen based vinyls such as vinyl chloride,vinylidene chloride, vinyl bromide, vinyl fluoride, vinylidene fluoride,and the like; vinyl esters such as vinyl propionate, vinyl acetate,vinyl benzoate, and the like; vinyl ethers such as vinyl methyl ether,vinyl ethyl ether, and the like; vinyl ketones such as vinyl methylketone, vinyl ethyl ketone, vinyl hexyl ketone, and the like; N-vinylcompounds such as N-vinylcarbazole, N-vinylindole, N-vinylpyrrolidone,and the like; vinyl compounds such as vinylnaphthalene, vinylpyridine,and the like; acrylic acid or methacrylic acid derivatives such asacrylonitrile, methacrylonitrile, acrylamide and the like. These vinylbased monomers may be employed individually or in combination.

Furthermore, still more preferably employed as polymerizable monomers,which constitute a resin, are those having an ionic dissociation groupin combination, which are, for example, have a substituent such as acarboxyl group, a sulfonic acid group, a phosphoric acid group, and thelike as a group constituting the substituent. Listed as specificexamples are acrylic acid, methacrylic acid, maleic acid, itaconic acid,cinnamic acid, fumaric acid, monoalkyl maleate, monoalkyl itaconate,styrenesulfonic acid, allylsulfosuccinic acid,2-acrylamide-2-methylpropanesulfonic acid, acidphosoxyethylmethacrylate, 3-chloro-2-acidphophoxypropyl methacrylate, and the like.

Further, the resin may be modified so as to have a cross-linkingstructure, employing multifunctional vinyls such as divinylbenzene,ethylene glycol dimethacrylate, ethylene glycol diacrylate, diethyleneglycol dimethacrylate, diethylene glycol diacrylate, triethylene glycoldimethacrylate, triethylene glycol diacrylate, neopentyl glycoldimethacrylate, neopentyl glycol diacrylate, and the like.

A radical polymerization initiator includes a water-soluble initiatorsuch as peroxide salt compound (for example, potassium peroxide,ammonium peroxide), salt of azobisaminodipropane acetic acid,azobiscyano valerate, azobiscyano valeric acid, and hydrogen peroxide.

A colorant such as carbon black, a magnetic material, a dye and apigment, is usable for the colorant of the toner.

Examples of the carbon black usable as the colorant include channelblack, furnace black, acetylene black, thermal black and lump black.

Examples of the magnetic substance include a ferromagnetic metal such asiron, nickel and cobalt, an alloy containing such the metal, a compoundof a ferromagnetic metal such as ferrite and magnetite, a ferromagneticalloy by a heat treatment even though containing no ferromagnetic metalsuch as a kind of alloy called Heuslar alloy such asmanganese-copper-aluminum and manganese-copper-tin, and chromiumdioxide.

As the dye, for example, C.I. Solvent Red series of 1, 49, 52, 58, 63,111, and 122, C.I. Solvent Yellow series of 19, 44, 77, 79, 81, 82, 93,98, 103, 104, 112 and 162, and C.I. Solvent Blue series of 25, 36, 60,70, 93 and 95, are usable. A mixture of them may also be used.

Examples of the pigment include C.I. Pigment Red series of 5, 48:1,53:1, 57:1, 122, 139, 144, 149, 166, 177, 178 and 222, C.I. PigmentOrange series of 31 and 43, C.I. Pigment Yellow series of 14, 17, 93, 94and 138, C.I. Pigment Green 7, C.I. Pigment Blue series of 15:3 and 60.These pigments may be used singly or in combination.

Number average of primary particle diameter of the colorant, which mayvary depending on the species, is preferably about 10 to 200 nm.

The amount of the colorant is not particularly specified as far as it issufficient to form images, and 1 to 10 weight percent in the Toner B ispreferable.

Examples of internal additive to be added in the toner include areleasing agent, a charge controlling agent, etc.

Practical examples of the releasing agent include polyolefin compoundssuch as low molecular weight polypropylene having number averagemolecular weight of 1,500 to 9,000, low molecular weight polyethylene,ethylene-propylene copolymer, microcrystaline wax, Carnauba wax, Sazolewax, parafin wax, amide wax etc.

Practical examples of the charge controlling agent include a negativecharge controlling agent an azo metal complex such as azo chromiumcomplex, a salicylic chromium complex, a salicylic zinc complex and acalixarene compound, a positive charge controlling agent such as aNigrosine dye and a quaternary ammonium salt, etc.

The employed coagulating agents are not particularly limited, howeverthose selected from metal salts are more suitable. Specific examplesinclude salts of univalent metals such as alkali metals, for example,sodium, potassium, lithium and the like; alkali earth metal salts ofdivalent metals such as calcium, magnesium, and the like; salts ofdivalent metals such as manganese, copper, and the like; and salts oftrivalent metals such as iron, aluminum, and the like. Listed asspecific salts can be sodium chloride, potassium chloride, lithiumchloride, calcium chloride, zinc chloride, copper sulfate, magnesiumsulfate, manganese sulfate, and the like. These may be employed incombination.

The added amount of the coagulant of the present invention is acceptableif it exceeds the critical coagulation concentration, and is preferablyat least 1.2 times of the critical coagulation concentration, and ismore preferably at least 1.5 times.

The critical coagulation concentration varies greatly depending on theemulsified components and dispersing agents themselves. For example, thecritical coagulation concentration is described in Seizo Okamoto, et al.“Kobunshi Kagaku (Polymer Chemistry)”, edited by Nihon Kobunshi Gakkai,whereby detailed critical coagulation concentration data can beobtained. Furthermore, as another method, ζ (zeta) potentials of aspecified particle dispersion are measured upon adding a desired salt tothe particle dispersion, while changing the salt concentration, and saidsalt concentration which varies the ζ potential can be obtained as thecritical coagulation concentration.

A solvent which is infinitely soluble denotes a solvent which isinfinitely soluble in water and as such solvents, those which do notdissolve the resin formed in the present invention are selected.Specifically, cited are alcohols such as methanol, ethanol, propanol,isopropanol, t-butanol, methoxyethanol, butoxyethanol, and the like,nitrites such as acetonitrile, and ethers such as dioxane. Inparticular, ethanol, propanol and isopropanol are preferred.

The added amount of such solvents which are infinitely soluble ispreferably between 1 and 100 percent by volume of the polymer containingdispersion to which the coagulant is added.

In such the method, the isolation ratio of the specified element can becontrolled by controlling the adding order and the adding time of thevarious raw materials, the polymerization condition of monomer, theaggregation condition of polymerized particles and the washing conditionafter reaction.

The polymerization method for preparing Toner B is not limited to anemulsion polymerization method, for example, a suspension polymerizationmethod or a solution polymerization method are also usable as long asthe isolation ratio of the specified element can be controlled to notmore than 10% by number.

The suspension polymerization method is a method by which apolymerizable monomer composition prepared by mixing a compoundcontaining the specified element such as the colorant, chargecontrolling agent or the magnetic substance, a polymerization initiatorand a polymerizable monomer. The composition is dispersed and suspendedin an aqueous medium and is subjected to the polymerization treatment.In such the case, an inorganic dispersion stabilizing agent such astricalcium phosphate and colloidal silica, and an organic dispersionstabilizing agent such as polyvinyl alcohol and gelatin, and asurfactant such as sodium dodecylbenzene-sulfonate may be used.

By the solution polymerization method, the monomer, polymerizationinitiator and the substance containing the specified element such as thecolorant, charge controlling agent and the magnetic substance aredissolved or dispersed in a solvent and the polymerization reaction isperformed by heating. In such the case, there is no limitation on thesolvent as long as the solvent can dissolve the monomer and the polymeror resin. Example of the solvent include acetone, methyl ethyl ketone,benzene, toluene, chloroform and THF.

As the polymerization initiator in the suspension polymerization methodand the solution polymerization method, an oil-soluble radicalpolymerization initiator such as azoisobutyronitrile and laurylperoxide, is usable. In the invention, it is preferred that the toner isprepared by the emulsion polymerization method, even though variousmethods can be utilized as above-mentioned. The reason of such the factis not confirmed but the emulsion polymerization method is preferably asthe preparation method of the polymerized toner in the invention sincean extreme small amount of isolated substance can be formed because thecompound containing the specified element is coagulated with the resinparticle in the aqueous medium to form a toner in this method.

In the toner for developing electrostatic image according to theinvention, the glass transition point of the binder resin measured by adifferential thermal analysis is preferable within the range of from 20°C. to 90° C.

The softening point of the binder resin measured by a Flowtester ispreferably within the range of from 80° C. to 220° C.

It is preferable that the binder resin has a number average molecularweight Mn of from 1,000 to 100,000, a weight average molecular weight Mwof from 2,000 to 1,000,000, and a molecular weight distribution Mw/Mn offrom 1.5 to 100, particularly 1.8 to 70.

In the toner for developing electrostatic image according to theinvention, various external additives may be added according tonecessity.

Known inorganic fine particles or organic fine particles may be added asthe external additive, and the addition of the inorganic fine particleis preferable from the viewpoint of giving a flowing ability to thecolored particle.

Various compounds such as various inorganic oxides, nitrides andboronide may be used as the substance constituting the inorganic fineparticle. Examples of such the compound include silica, alumina,titania, zirconia, barium titanate, aluminum titanate, strontiumtitanate, magnesium titanate, calcium titanate, zinc oxide, chromiumoxide, cerium oxide, antimony oxide, tungsten oxide, tin oxide,tellurium oxide, manganese oxide, boron oxide, silicon carbide, boroncarbide, titanium carbide, silicon nitride, titanium nitride and boronnitride.

The number average primary particle diameter of the inorganic fineparticle to be used as the external additive is preferably from 10 to500 nm. The number average primary particle diameter of the inorganicfine particle is measured by the analysis of image obtained by electronmicroscopic observation using a transmission electron microscope.

The surface of the inorganic fine particle is preferably subjected to ahydrophobilizing treatment using a coupling agent such as a titaniumcoupling agent and a silane coupling agent, a silicone oil, a metal saltof fatty acid such as aluminum stearate, zinc stearate and calciumstearate.

<Developer>

The developer according to the invention contains the above-mentionedtoner, which may be a single-component developer comprising a magnetictoner containing a magnetic substance or a non-magnetic toner containingno magnetic substance, or a two-component developer comprising the tonerand a carrier.

In the case of the two-component developer, the carrier may be a carriercomposed of magnetic substance particle only, or a resin coated carrierwhich is composed of a core particle composed of a magnetic substanceand a resin covering the core particle.

The size of the carrier is preferably from 20 to 150 μm, preferably from20 to 100 μm in volume average diameter.

As the raw material of the core particle, iron, ferrite and magnetiteare usable.

As the resin for making the resin coated carrier, a known resin such asa silicone resin, a styrene-acryl resin and a fluorine-containingacrylic acid ester may be used without any limitation.

The image forming method according to the invention comprises the stepsof forming an electrostatic image on the surface of a photoreceptor,developing the electrostatic image by a developer to form a toner imageon the surface of photoreceptor, transferring the toner image to arecording medium and fixing the transferred toner image, in which theabove-mentioned toner is used.

A contact developing method in which a developer layer formed on adeveloper transportation carrying member is contacted with thephotoreceptor, and a non-contact developing method, in which thedeveloper layer is not contacted with the photoreceptor, are eitherusable as the method for developing the electrostatic image.

(1) Contact Developing Method

When the contact developing method is performed, the thickness of thedeveloper layer formed on the developer transportation carrying memberis preferably from 0.1 to 8 mm, more preferably from 0.4 to 5 mm, in thedeveloping zone.

The space between the photoreceptor and the developer transportationcarrier member is preferably from 1.5 to 7 mm, more preferably from 0.2to 4 mm.

(2) Non-Contact Developing Method

FIG. 1 shows a scheme of a developing section for the non-contactdeveloping method which can suitably be applied for image forming methodof the invention. In the drawing, 1 is the photoreceptor, 2 is thedeveloper transportation carrying member, 3 is the two-componentdeveloper according to the invention, 4 is a developer amount regulatingmember, 5 is a developing zone, 6 is a thin layer of the developer, and7 is a power source to apply an alternating electric field.

The developer transportation carrying member 2 is a developing devicehaving a developing sleeve 2A and a magnet 2B, and the surface of thedeveloper transportation carrying member 2 is constituted by a materialsuch as aluminum, anodized aluminum and a stainless steel.

The diameter of the developer transportation carrying member 2 ispreferably from 10 to 40 mm. When the diameter is too small, thesufficient contact for giving an electric charge to the tonerdifficultly obtained, and when the diameter is too large, a problem oftoner scattering is raised since the centrifugal force is increased.

The two-component developer 3 is carried by magnetic force on thedeveloper transportation carrying member 2 which has the magnet 2B, andtransported into the developing zone 5 by the move of the developingsleeve 2A.

The thickness of the thin layer of the developer 6 transported into thedeveloping zone 5 is regulated by the pressure of the developer amountregulating member 4 so that the developer layer does not contact to thephotoreceptor.

The thickness of the developer layer 6 in the developing zone 5 ispreferably from 20 to 500 μm.

The pressure of the developer amount regulating member is preferablyfrom 1 to 15 gf/mm, more preferably from 3 to 10 gf/mm. When thepressure is too small, the transportation tends to be instable since theregulation force is insufficient. On the other hand, when the pressureis too large, the durability of the developer tends to be lowered sincethe stress to the developer is increased.

A urethane blade and a phosphor bronze plate may be used as thedeveloper amount regulating member.

The minimum space D_(sd) in the developing zone 5 is, for exampleapproximately from 100 to 1000 μm which is larger than the thickness ofthe developer layer 6, preferably from 20 to 500 μm, transported intothe developing zone 5.

The power source 7 for applying the alternating electric field ispreferably a power source supplying an alternative current of afrequency of from 1 to 10 kHz and a voltage of from 1 to 3 kV_(p-p). Thepower source may be one supplying an alternating current overlapped witha direct current. The voltage of the direct current is preferably from300 to 800 V. When a bias voltage is applied for developing process,both of a method applying only direct current and that applying analternative current may applicable.

When the image forming method of the invention is utilized for forming acolor image, both of (1) a successive transfer method by which mono-toneimage is successively formed on the photoreceptor and transferred one byone onto an image supporting sheet and (2) a collective transfer methodby which plural mono-tone images are developed the photoreceptor to forma color image and the color image is collectively transferred to theimage supporting sheet, may be usable, and the method of (2) ispreferable from the viewpoint of inhibiting the deviation of colorimages.

EXAMPLES

The examples of the invention are described below in concrete. However,the embodiment of the invention is not limited to the examples.

(1) Preparation of Toner

Examples 1 to 4, 6 and 16 and Comparative Examples 1 to 2

A binder resin, a colorant, a mold releasing agent and a chargecontrolling agent were previously mixed according to the receipt shownin Table 1. The mixture was molten, kneaded, crushed and classified toprepare a colored, particle. In such the procedure, the conditions ofthe crushing and the classifying were controlled while measuring theisolation ratio of the specified element. The external additives shownin Table 1 is added and mixed with the colored particle the prepare thetoners of the invention and the comparative toners.

The silica and titanium oxide used as the external additives were eachpreviously subjected to a hydrophobilizing treatment. The isolationratio of the toner treated above was measured.

TABLE 1 Comparative Example example 1 2 3 4 6 16 1 2 Receipt of BinderStyrene-acrylate 100 100 100 100 100 100 raw material resin resin 1composition Styrene-acrylate of colored resin 2 particle Polyester resin100 100 (Parts by Colorant Magnetite 105 105 105 105 105 weight) Copper3 phthalocyanine type cyan pigment Quinacridone magenta type pigmentBenzidine yellow type pigment Carbon black 10 10 Mold Low molecular 3.53.5 4 3.5 4 4 releasing weight agent polypropylene Low molecular 3 4weight polyethylene Fatty acid amide wax Charge Iron-azo complex 1 1 10.7 1 1 control- Chromium ling agent salicylic acid complex Zincsalicylic acid complex Molybdenum 2 quaternary ammonium complex Externaladditive (added Silica 1 1 1 1 2.5 1 25 amount to colored par-Positively 1 ticle in parts by weight) chargeable silica Titanium oxide0.5 0.5

Example 17

Into a solution composed of 270 ml of water, 3 g of a nonionicemulsifying agent, 4.5 g of an anionic emulsifying agent and 6 g ofpotassium persulfate, 220 g of styrene monomer, 40 g of butyl acrylateand 12 g of acrylic acid were added and reacted for 8 hours at 70° C.while stirring to polymerize. Thus an emulsion of polymer particles wasobtained. To the emulsion, 11 g of a copper phthalocyanine type cyanpigment, 60 g of a polypropylene emulsion having a solid componentcontent of 30% by weight and 1620 ml of purified water were added. Themixture was maintained at 30° C. for 2 hours while stirring anddispersing by a slusher. Moreover, the emulsion was heated by 70° C. andmaintained at this temperature for 3 hours while stirring. Then theemulsion was cooled and filtered. Thus obtained solid product waswashed, dried and crushed to obtain colored particles.

To 100 parts by weight of the colored particles, 2.5 parts by weight ofsilica and 0.5 parts by weight of titanium oxide were added as externaladditives and mixed to prepare a toner according to the invention. Thesilica and the titanium oxide used as the external additives were eachpreviously subjected to a hydrohobilizing treatment.

Example 18

Into a solution composed of 600 ml of purified water and 5.0 g of sodiumdodecylsulfate, 11 g of a copper phthalocyanine type cyan pigment wasadded, and the mixture was stirred while applying ultrasonic wave tosufficiently disperse the cyan pigment. Thus a dispersion was prepared.

Besides, a low molecular weight polypropylene was emulsified in waterwhile heating to prepare an emulsifying dispersion having a solidcomponent content of 30% by weight.

The dispersion containing the copper phthalocyanine type cyan pigmentwas mixed with the emulsifying dispersion containing the lower molecularweight polypropylene. To the mixture, 220 g of styrene monomer, 40 g ofn-butyl acrylate monomer, 12 g of methacrylic acid monomer, 5.4 g oft-dodecylmercaptane and 1620 ml of deaerated water were added, and themixture was heated by 70° C. under a nitrogen gas current whilestirring. Emulsion polymerization was performed by adding a solutioncomposed of 440 ml of water in which 4.3 g of potassium persulfate wasdissolved and maintaining at 70° C. for 3 hours.

To 1000 ml of the polymerizing liquid thus obtained, sodium hydroxidewas added to adjust the pH to 9.5. Then 270 ml of a 2.2 mole-% solutionof potassium chloride and a solution composed of 67 ml of waterdissolved therein 160 ml of isopropyl alcohol, 9.0 g ofpolyoxyethyleneoctylphenyl ether having an average polymerization degreeof 10 were further added. Thus obtained reacting liquid was maintainedat 75° C. and stirred for 6 hours.

Thereafter, the reacting liquid was filtered. The solid composition waswashed 3 times by a mixture of methanol and water in a ratio of 1:1, anddried and crushed to prepare colored particles.

To 100 parts by weight of the colored particles, 2.5 parts by weight ofsilica and 0.5 parts by weight of titanium oxide were added as externaladditives and mixed to prepare a toner according to the invention. Thesilica and the titanium oxide used as the external additives were eachpreviously subjected to a hydrohobilizing treatment.

Comparative Example 3

To a solution composed of 270 ml of purified water, dissolved therein, 3g of nonionic emulsifying agent 4.5 g of an anionic emulsifying agentand 6 g of potassium persulfate, 220 g of styrene monomer, 40 g of butylacrylate and 12 g of acrylic acid were added. The mixture waspolymerized at 70° C. for 8 hours while stirring to obtain an emulsion.To the emulsion, 11 g of a copper phthalocyanine type cyan pigment, 60 gof a polypropylene emulsion having a solid composition content of 30% byweight and 1620 ml of purified water were added. The emulsion wasmaintained at 30° C. for 0.5 hours while dispersing and stirring by aslusher. Then the mixture was heated by 70° C. and stirred for 3 hours.Thereafter, the emulsion was cooled and filtered to separate the solidcomposition. The solid composition was washed by water, dried andcrushed to prepare colored particles.

To 100 parts by weight of the colored particles, 2.5 parts by weight ofsilica and 0.5 parts by weight of titanium oxide were added as externaladditives and mixed to prepare a toner according to the invention. Thesilica and the titanium oxide used as the external additives were eachpreviously subjected to a hydrohobilizing treatment.

The kind, the content and the isolation ratio of the specified elementcontained in the toners of Examples 1 to 18 and Comparative Examples 1to 3 are shown in Table 2.

The measurement of such the values were carried out by the use ofParticle Analyzer, manufactured by Yokogawa Denki Co., Ltd., under thefollowing conditions.

Detected number of C: Approximately 1500

Noise cutting level: Not more than 1.5

Sorting time: 20 digits

Gas: 0.1% of ozone, Helium gas

The data of the whole particles measured under the following conditionswere plotted on a graph in which the horizontal axis showed the lightemission voltage caused by carbon and the vertical axis showed the lightemission voltage caused by the specified element. The number ofparticles plotted at the position of light emission voltage caused bycarbon was zero was counted and the percentage of number of such theparticle to the whole number of the particles measured was calculated.

(2) Preparation of Developer

The toners prepared in Examples 1 to 4 and Comparative example 1 wereeach used as a one-component developer.

Besides, two-component developers each having a toner content of 8% wereprepared using the toners of Examples 6 and 16 to 18 and ComparativeExamples of 2 to 3 using carrier 1 or 2 each composed of core particleshaving an average diameter of 45 μm coated with styrene-acryl resin, ofcarrier 3 composed of core particles having an average diameter of 45 μmcoated with a silicone resin according to Table 2.

(3) Image Formation

Practical printing tests of 10,000 sheets of image information having aimage area ratio of 5% were performed using each of the one-componentdeveloper relating to Examples 1 to 4 and Comparative example 1 by aprinter KL2010, manufactured by Konica Corporation, which was modifiedso as to be fitted to the development by the one-component developer.The charged amount of the toner was measured at the initial time and,and the image after 100,000 sheets of printing was visually observed tocheck the formation of fog.

One the other hand, practical printing tests of 10,000 sheets of imageformation having a image area ratio of 5% were performed using each oftwo-component developer relating to Examples 6 and 16 to 18 andcomparative examples 2 and 3 by a printer KL2010, manufactured by KonicaCorporation, which was modified so as to be fitted to the development bythe two-component developer. The charged amount of the toner wasmeasured at the initial time, and the image after 100,000 sheets ofprinting was visually observed to check the formation of fog at thebackground of the image.

The results of the tests are shown in Table 2.

TABLE 2 Specific element Charging in toner amount Content Iso- AfterForma- (% by lated Kind of Initial 10,000 tion Kind weight) ratiocarrier time printing of fog Example 1 Fe 33.9 0.5 — −5.3 −5.1 NoneExample 2 Fe 34.0 5.2 — −5.3 −4.2 None Example 3 Fe 33.5 3.1 — −5.2 −4.5None Example 4 Fe 33.8 0.3 — −4.1 −4.1 None Example 6 Cu 0.29 8.6carrier 2 −20.7 −15.8 None Example 16 Mo 0.80 1.7 carrier 1 23.5 −22.2None Example 17 Cu 0.39 5.0 carrier 1 −22.4 −19.1 None Example 18 Cu0.39 1.4 carrier 1 −23.7 −22.7 None Comparative Fe 33.3 12.3 — −5.2 −2.1Fog Example 1 Found Comparative Fe 0.29 10.5 carrier 1 −22.1 −13.2 FogExample 2 Found Carparative Cu 0.38 11.4 carrier 2 −23.7 −12.9 FogExample 3 Found

As is shown in Table 2, it is confirmed that the lowering in the chargedamount of the toner is small after continuous image formation and theimage can be stably formed when the toners relating to Examples 1through 18 were used, since in each of the toners the isolation ratio ofthe specified element is not more than 10% by number.

The change in the charging property caused by contamination of thecharge providing member is inhibited when the image formation iscontinued for a long period of time, and stable images are formed formany times of image formation by the toner for developing electrostaticimage according to the invention.

The change in the charging property caused by contamination of thecharge providing member is inhibited when the image formation iscontinued for a long period of time, and stable images are formed formany times of image formation by the developer for developingelectrostatic image according to the invention.

The change in the charging property caused by contamination of thecharge providing member is inhibited when the image formation iscontinued for a long period of time, and stable images are formed formany times of image formation by the image forming method for developingelectrostatic image according to the invention.

1. A toner for developing an electrostatic image, comprising: a resinbinder and, not less than 0.1% by weight of an element which is providedin the form of a colorant pigment comprising copper phthalocyaninewherein the element is copper; wherein the toner has an isolation ratioof the element of not more than 10% and greater than 0.1% by number;where the isolation ratio of the element is determined by measuringlight emission voltage caused by carbon and the element of particlespresent in the toner with a fluorescent X-ray analysis and defined as100 times the number of particles exhibiting emission from the elementbut not exhibiting emission from carbon divided by the sum of the numberof particles exhibiting emission from the element but not exhibitingemission from carbon and the number of particles exhibiting emissionfrom the element and exhibiting emission from carbon, and wherein thecolorant pigment has an average primary particle diameter of 10 to 200nm, and the resin binder has an Mn of 1,000 to 100,000, an Mw of 2,000to 1,000,000, and a molecular weight distribution (Mw/Mn) of 1.5 to 100.2. The toner of claim 1, wherein the toner is prepared by emulsionpolymerization.
 3. A developer for developing electrostatic imagecomprising a toner of claim
 1. 4. A developer for developingelectrostatic image comprising a toner of claim 1 and a carrier.
 5. Thetoner of claim 1, wherein the molecular weight distribution (Mw/Mn) is1.8 to
 70. 6. An image forming method comprises the steps of forming anelectrostatic image on the surface of a photoreceptor, developing theelectrostatic image by a developer to form a toner image, transferringthe developed toner image to a recording medium, and fixing the tonerimage transferred on the recording medium, wherein the developercomprises the toner of claim
 1. 7. The method of claim 6, whereindeveloping is performed with a non-contact method in which a developerlayer is not contacted with the surface of the photoreceptor.